Many ore bodies containing precious metals and precious stones are found in complex deposits, such as sedimentary, alluvial, oxidized volcanic bodies and laterites, which also contain clay. Such ore bodies are usually mixed with water, the coarse material screened out, and the resultant concentrate treated in a further process where precious metals and/or precious stones are recovered. Although this procedure works fairly well, it has been found that the clay content often forms balls which plug the screens and generally interfere with the recovery process. It is known that the clay balls encapsulate appreciable quantities of precious metal particles and precious stones which are lost in reject tailings. Precious metal particles and small precious stones are thus then present in suspension with clay particles in tailings ponds.
So far as is known, the problem of preventing the formation of clay balls and recovering such suspended precious metal and/or precious stones has not yet been solved in a cost effective manner. Attempts have been made to solve the problem by massive dilution with water or separate processing of the clay balls. However, both of these procedures are expensive and time consuming.
It is therefore an object of the invention to provide a cost effective process for recovering precious metal particles and small precious stones from aqueous clay suspensions containing such particles in suspension with the clay particles.
The present invention is based on the discovery that precious metal particles and/or precious stones can be separated from the clay particles in the suspension by means of a deflocculating agent.
According to the invention, a sufficient amount of deflocculating agent is added to cause deflocculation of the clay particles, allowing the deflocculated suspension to settle, and the settled material containing the precious metal particles and/or small precious stones is recovered.
The aqueous clay suspension may contain from about 1 to about 40% clay by weight, and the deflocculation agent may comprise sodium tripolyphosphate. The weight of sodium tripolyphosphate added may be from about 0.03 to about 1% of the dry weight of clay in the suspension.
The gold particles may have a size in the range of from about 0.1 to about 5 millimeters. The precious stones may comprise diamonds, sapphires or rubies. The diamonds may have a size in the range of from about 0.5 to about 10 millimeters, the sapphires may have a size in the range of from about 5 to about 30 millimeters, and the rubies may have a size in the range of from about 5 to about 30 millimeters.